Electrosurgical instruments have been used for many years in the field of high frequency surgery to coagulate or cut biological tissue. For coagulation, a high frequency current is passed through the tissue being treated so that it changes, due to protein clotting and dehydration. The tissue contracts so that the vessels are closed and thus, bleeding is stopped. Following coagulation, the tissue can be completely separated without bleeding, either using a high frequency current or by mechanical means.
Electrosurgical processes can be carried out using unipolar or bipolar techniques. With the unipolar technique, the current path usually leads from the electrosurgical instrument via the tissue being treated to a neutral electrode and from there back to a high-frequency (HF) generator. However, bipolar instruments are increasingly gaining importance. These are constructed having two sections that are electrically insulated from one another. The current path between the electrode parts can be calculated and does not run long distances through the body of the patient. This reduces the effects, for example, on cardiac pacemakers and other devices that are attached to the patient during the operation.
Bipolar instruments usually have two branches joined in an articulated manner to one another. At their proximal end, gripping devices are provided for manipulating the branches. At the distal ends of the branches, electrode parts are provided for grasping tissue and conducting the high frequency current through the tissue. The current supplied by an HF generator is conducted via current supply lines to the electrode parts of the bipolar instrument.
Laparoscopic instruments are similarly constructed. They are tubular shafted instruments wherein the movement of the branches is transmitted via a deflecting mechanism, arranged in the interior of the tubular shaft, to the electrode parts arranged at the distal end of the tubular shaft. The branches are extended by means of the deflecting mechanism such that the electrode parts can be introduced via the tubular shaft into body cavities (e.g. the abdominal cavity) and actuated from “outside.” This means that the proximal ends of the branches or the proximal region of the branches are transferred via the deflecting mechanism to the distal ends or the distal region of the branches with the electrode parts.
Unipolar instruments can be used for open surgery as well as for minimally invasive interventions (usually endoscopy).
In order to achieve reliable thermofusion of biological tissues, a variety of conditions must be observed. It must be possible to hold the tissue, for example, a blood vessel, reliably between the electrode parts to prevent it from slipping away. It is therefore required that a certain pressure is exerted on the tissue via the electrode parts. Furthermore, it must also be ensured that the electrode parts cannot be brought closer together than a minimum spacing, in order to avoid an unwanted short-circuit between the electrode parts.
In order to be able to perform a coagulation or a cutting procedure, the known instruments are connected to switches, for example, hand or foot switches. With these, the high frequency current which is fed to the tissue being treated can be activated.
With the aforementioned instruments, coagulation and/or cutting operations can be triggered at unfavourable time points by unintended actuation of the switches. The branches are often not completely closed and the tissue is not properly held between the branches, although current is already being fed to the tissue. This results, for example, in incomplete thermofusion, which can lead to dangerous after-bleeding or coagulation at unwanted sites. With unipolar instruments, current supply at an unfavourable time point can also bring about damage to the tissue being treated.
Furthermore, hand or foot switches require additional space and cause the instrument and the whole operation area to become more cluttered.
It is therefore an object of the invention to provide an electrosurgical instrument of the aforementioned type such that it can be produced easily and economically, and such that a surgical intervention can be easily and reliably performed with the instrument.